Pressure sensing guidewire and methods for calculating fractional flow reserve

ABSTRACT

Medical devices and methods for making and using medical devices are disclosed. An example method may include a method for calculating fractional flow reserve including providing a pressure sensing guidewire, advancing the pressure sensing guidewire through a blood vessel to a first position distal of an intravascular occlusion, determining a distal pressure within the body lumen with the pressure sensing guidewire, proximally shifting the pressure sensing guidewire to a second position proximal of the occlusion, determining a proximal pressure within the body lumen with the pressure sensing guidewire, measuring an aortic pressure, and calculating a pressure drift. The pressure drift may be the difference between the aortic pressure and the proximal pressure. The method may also include calculating a drift-compensated fractional flow reserve. The drift-compensated fraction flow reserve may correspond to (the distal pressure+the pressure drift) divided by the aortic pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/890,657, filed Oct. 14, 2013, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and methods for manufacturing medical devices. More particularly, the present disclosure pertains to blood pressure sensing guidewires and methods for using pressure sensing guidewires.

BACKGROUND

A wide variety of intracorporeal medical devices have been developed for medical use, for example, intravascular use. Some of these devices include guidewires, catheters, and the like. These devices are manufactured by any one of a variety of different manufacturing methods and may be used according to any one of a variety of methods. Of the known medical devices and methods, each has certain advantages and disadvantages. There is an ongoing need to provide alternative medical devices as well as alternative methods for manufacturing and using medical devices.

BRIEF SUMMARY

This disclosure provides design, material, manufacturing method, and use alternatives for medical devices. An example method may include a method for calculating fractional flow reserve including providing a pressure sensing guidewire, advancing the pressure sensing guidewire through a blood vessel to a first position distal of an intravascular occlusion, determining a distal pressure within the body lumen with the pressure sensing guidewire, proximally shifting the pressure sensing guidewire to a second position proximal of the occlusion, determining a proximal pressure within the body lumen with the pressure sensing guidewire, measuring an aortic pressure, and calculating a pressure drift. The pressure drift may be the difference between the aortic pressure and the proximal pressure. The method may also include calculating a drift-compensated fractional flow reserve. The drift-compensated fraction flow reserve may correspond to (the distal pressure+the pressure drift) divided by the aortic pressure.

Another example method for calculating fractional flow reserve may include providing a pressure sensing guidewire, advancing the pressure sensing guidewire through a body lumen of the patient to a first position proximal of an intravascular occlusion, determining a first proximal pressure within the body lumen with the pressure sensing guidewire, measuring an aortic pressure within a patient, equalizing the first proximal pressure with the aortic pressure, advancing the pressure sensing guidewire to a distal position that is distal of the intravascular occlusion, determining a distal pressure within the body lumen with the pressure sensing guidewire, proximally shifting the pressure sensing guidewire to the first position, determining a second proximal pressure within the body lumen with the pressure sensing guidewire, and calculating a pressure drift. The pressure drift may be the difference between the second proximal pressure and the aortic pressure. The method may also include calculating drift-compensated fractional flow reserve. The drift-compensated fraction flow reserve may correspond to (the distal pressure+the pressure drift) divided by the second aortic pressure.

Fractional flow reserve systems are also disclosed. An example fractional flow reserve system may include a pressure sensing guidewire including a pressure sensor and a control unit capable of processing pressure information from the pressure sensor and outputting a drift-compensated fractional flow reserve corresponding to (a downstream pressure measured by the pressure sensor+a pressure drift) divided by an aortic pressure of a patient.

The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:

FIG. 1 is a partial cross-sectional side view of a portion of an example medical device;

FIG. 2 is a partial cross-sectional view of an example medical device disposed at a first position adjacent to an intravascular occlusion;

FIG. 3 is a partial cross-sectional view of an example medical device disposed at a second position adjacent to an intravascular occlusion; and

FIG. 4 is a flow chart schematically depicting an example method.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification.

All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include one or more particular features, structures, and/or characteristics. However, such recitations do not necessarily mean that all embodiments include the particular features, structures, and/or characteristics. Additionally, when particular features, structures, and/or characteristics are described in connection with one embodiment, it should be understood that such features, structures, and/or characteristics may also be used connection with other embodiments whether or not explicitly described unless clearly stated to the contrary.

The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.

During some medical interventions, it may be desirable to measure and/or monitor the blood pressure within a blood vessel. For example, some medical devices may include pressure sensors that allow a clinician to monitor blood pressure. Such devices may be useful in determining fractional flow reserve (FFR), which may be understood as the pressure after a stenosis relative to the pressure before the stenosis (and/or the aortic pressure). In some instances, the measurements made by a pressure sensing guidewire may consistent and precise. However, in other instances, the pressure readings may tend to “drift”. For example, one or more initial pressure readings may have a certain level of precision and subsequent pressure readings could begin to be less precise. Disclosed herein are a number of medical device that include pressure sensing capabilities and may be capable of accounting for the possibility of pressure drift. Furthermore, disclosed herein are methods for calculating FFR which take into account the possible of drift.

FIG. 1 illustrates a portion of an example medical device 10. In this example, medical device 10 is a blood pressure sensing guidewire 10. However, this is not intended to be limiting as other medical devices are contemplated including, for example, catheters, shafts, leads, wires, or the like. Guidewire 10 may include a guidewire shaft or tubular member 12. Tubular member 12 may include a proximal portion 14 and a distal portion 16. The materials for proximal portion 14 and distal portion 16 may vary and may include those materials disclosed herein. For example, distal portion 16 may include a nickel-cobalt-chromium-molybdenum alloy (e.g., MP35-N). Proximal portion 14 may include stainless steel. These are just examples. Other materials may also be utilized.

In some embodiments, proximal portion 14 and distal portion 16 are formed from the same monolith of material. In other words, proximal portion 14 and distal portion 16 are portions of the same tube defining tubular member 12. In other embodiments, proximal portion 14 and distal portion 16 are separate tubular members that are joined together. For example, a section of the outer surface of portions 14/16 may be removed and a sleeve 17 may be disposed over the removed sections to join portions 14/16. Alternatively, sleeve 17 may be simply disposed over portions 14/16. Other bonds may also be used including welds, thermal bonds, adhesive bonds, or the like. If utilized, sleeve 17 used to join proximal portion 14 with distal portion 16 may include a material that desirably bonds with both proximal portion 14 and distal portion 16. For example, sleeve 17 may include a nickel-chromium-molybdenum alloy (e.g., INCONEL).

A plurality of slots 18 may be formed in tubular member 12. In at least some embodiments, slots 18 are formed in distal portion 16. In at least some embodiments, proximal portion 14 lacks slots 18. However, proximal portion 14 may include slots 18. Slots 18 may be desirable for a number of reasons. For example, slots 18 may provide a desirable level of flexibility to tubular member 12 (e.g., along distal portion 16) while also allowing suitable transmission of torque. Slots 18 may be arranged/distributed along distal portion 16 in a suitable manner including any of those arrangements disclosed herein. For example, slots 18 may be arranged as opposing pairs of slots 18 that are distributed along the length of distal portion 16. In some embodiments, adjacent pairs of slots 18 may have a substantially constant spacing relative to one another. Alternatively, the spacing between adjacent pairs may vary. For example, more distal regions of distal portion 16 may have a decreased spacing (and/or increased slot density), which may provide increased flexibility. In other embodiments, more distal regions of distal portion 16 may have an increased spacing (and/or decreased slot density). These are just examples. Other arrangements are contemplated.

A pressure sensor 20 may be disposed within tubular member 12 (e.g., within a lumen 22 of tubular member 12). While pressure sensor 20 is shown schematically in FIG. 1, it can be appreciated that the structural form and/or type of pressure sensor 20 may vary. For example, pressure sensor 20 may include a semiconductor (e.g., silicon wafer) pressure senor, piezoelectric pressure sensor, a fiber optic or optical pressure sensor, a Fabry-Perot type pressure sensor, an ultrasound transducer and/or ultrasound pressure sensor, a magnetic pressure sensor, a solid-state pressure sensor, or the like, or any other suitable pressure sensor.

As indicated above, pressure sensor 20 may include an optical pressure sensor. In at least some of these embodiments, a fiber optic cable 24 may be attached to pressure sensor 20 and may extend proximally therefrom. An attachment member 26 may attach fiber optic cable 24 to tubular member 12. Attachment member 26 may be circumferentially disposed about and attached to fiber optic 24 and may be secured to the inner surface of tubular member 12 (e.g., distal portion 16). In at least some embodiments, attachment member 26 is proximally spaced from pressure sensor 20. Other arrangements are contemplated.

In at least some embodiments, distal portion 16 may include a region with a thinned wall and/or an increased inner diameter that defines a housing region 52. In general, housing region 52 is the region of distal portion 16 that ultimately “houses” the pressure sensor (e.g., pressure sensor 20). By virtue of having a portion of the inner wall of tubular member 12 being removed at housing region 52, additional space may be created or otherwise defined that can accommodate sensor 20.

In at least some embodiments, it may be desirable for pressure sensor 20 to have reduced exposure along its side surfaces to fluid pressure (e.g., from the blood). Accordingly, it may be desirable to position pressure sensor 20 along a landing region 50 defined along housing region 52. Landing region 50 may be substantially free of slots 18 so that the side surfaces of pressure sensor 20 have a reduced likelihood of being deformed due to fluid pressures at these locations. Distal of landing are 50, housing region 52 may include slots 18 that provide fluid access to pressure sensor 20.

Moreover, slots 18 may define a fluid pathway that allows blood (and/or a body fluid) to flow from a position along the exterior or outer surface of guidewire 10 (and/or tubular member 12), through slots 18, and into the lumen 22 of tubular member 12, where the blood can come into contact with pressure sensor 20. Because of this, no additional side openings/holes (e.g., other than slots 18) may be necessary in tubular member 12 for pressure measurement. This may also allow the length of distal portion 16 to be shorter than typical sensor mounts or hypotubes that would need to have a length sufficient for a suitable opening/hole (e.g., a suitable “large” opening/hole) to be formed therein that provides fluid access to sensor 20.

A tip member 30 may be coupled to distal portion 16. Tip member 30 may include a shaping member 32 and a spring or coil member 34. A distal tip 36 may be attached to shaping member 32 and/or spring 34. In at least some embodiments, distal tip 36 may take the form of a solder ball tip. Tip member 30 may be joined to distal portion 16 of tubular member 12 with a bonding member 46 such as a weld.

Tubular member 12 may include a hydrophilic coating 19. In some embodiments, hydrophilic coating 19 may extend along substantially the full length of tubular member 12. In other embodiments, one or more discrete sections of tubular member 12 may include hydrophilic coating 19.

In use, a clinician may use guidewire 10 to measure and/or calculate FFR (e.g., the pressure after an intravascular occlusion relative to the pressure before the occlusion and/or the aortic pressure). Measuring and/or calculating FFR may include advancing guidewire 10 through a blood vessel or body lumen 54 to a position that is proximal or upstream of an occlusion 56 as shown in FIG. 2. For example, guidewire 10 may be advanced through a guide catheter 58 to a position where at least a portion of sensor 20 is disposed distal of the distal end of guide catheter 58 and measuring the pressure within body lumen 54. This pressure may be characterized as the proximal pressure. In at least some embodiments, the proximal pressure may be “equalized” with an aortic pressure. For example, the proximal pressure measured by guidewire 10 may be set to be the same as a measured aortic pressure. The aortic pressure (e.g., a measured aortic pressure) may be the pressure measured within the aorta (or at another suitable location) by another device (e.g., a pressure sensing guidewire, catheter, or the like).

Guidewire 10 may be further advanced to a position distal or downstream of occlusion 56 as shown in FIG. 3 and the pressure within body lumen 54 may be measured. This pressure may be characterized as the downstream or distal pressure.

As indicated above, pressure sensors like pressure sensor 20 may be generally precise. However, in some instances a “pressure drift” may occur where the pressure readings made by pressure sensor 20 “drifts” away from a previous reading. If pressure drift does occur, the calculated fractional flow reserve may be inaccurate. It may be desirable to periodically check for and account for any pressure drift that may occur.

In order to take into account or otherwise monitor for pressure drift, guidewire 10 may be proximally retracted to a position proximal of occlusion 56 (e.g., as shown in FIG. 2) and the pressure within body lumen 54 may be measured. This pressure may be characterized as a second proximal pressure. Optionally, the aortic pressure may also be measured a second time. In some embodiments, the second proximal pressure may be compared to the aortic pressure (e.g., the aortic pressure as measured the first time or as measured the second time). Any differences that may be present may be defined as the “pressure drift”. For the purposes of this disclosure, the pressure drift may be understood as observed changes in a pressure due to shifting precision of the sensor. For example, the pressure drift may be a value corresponding to the aortic pressure (e.g., the aortic pressure as measured the first time or as measured the second time) minus the second proximal pressure. When taking into account the pressure drift, the drift-compensated FFR may be output as the (distal pressure+the pressure drift) divided by the aortic pressure (e.g., the aortic pressure as measured the first time or as measured the second time).

An overview of the example method including compensation for pressure drift is schematically illustrated in FIG. 4. For example, box 60 indicates that pressure sensor 20 may be aligned with the distal end of guide catheter 58. This may include disposing at least a portion of pressure sensor 20 at or distal of the distal end of guide catheter 58 (e.g., as shown in FIG. 2). As indicated in box 62, pressure sensor 20 may be utilized to measure the proximal pressure. The measured proximal pressure may be equalized with the aortic pressure (e.g., the aortic pressure measured using another device as described herein). As indicated in box 64, guidewire 10 may be advanced distally beyond occlusion 56 (e.g., as shown in FIG. 3). As indicated in box 66, the distal pressure downstream of occlusion 56 may be measured. The measured aortic pressure and the distal pressure may be used to calculate FFR as indicated by box 68.

In order to compensate for pressure drift, guidewire 10 may be proximally retracted to a position proximal of occlusion 56. This may include proximally retracting guidewire 10 so that pressure sensor 20 is at or distal of the distal end of guide catheter 58 (e.g., as shown in FIG. 2) as indicated by box 70. As indicated by box 72, guidewire 10 may be used to check for drift. This may include measuring a second proximal pressure and comparing it with the aortic pressure (e.g., which may be measured again for comparison). The drift may be understood as the difference between the first proximal pressure (equalized with the aortic pressure) and the second proximal pressure. Finally, the drift-compensated FFR value can be calculated as (the distal pressure+the pressure drift) divided by the aortic pressure. The drift-compensated FFR value may be displayed on a suitable display unit. The actual numbers displayed on the display unit may include FFR and drift-compensated FFR.

The materials that can be used for the various components of guidewire 10 (and/or other guidewires disclosed herein) and the various tubular members disclosed herein may include those commonly associated with medical devices. For simplicity purposes, the following discussion makes reference to tubular member 12 and other components of guidewire 10. However, this is not intended to limit the devices and methods described herein, as the discussion may be applied to other similar tubular members and/or components of tubular members or devices disclosed herein.

Tubular member 12 may be made from a metal, metal alloy, polymer (some examples of which are disclosed below), a metal-polymer composite, ceramics, combinations thereof, and the like, or other suitable material. Some examples of suitable metals and metal alloys include stainless steel, such as 304V, 304L, and 316LV stainless steel; mild steel; nickel-titanium alloy such as linear-elastic and/or super-elastic nitinol; other nickel alloys such as nickel-chromium-molybdenum alloys (e.g., UNS: N06625 such as INCONEL® 625, UNS: N06022 such as HASTELLOY® UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and the like), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® 400, NICKELVAC® 400, NICORROS® 400, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 such as HASTELLOY® ALLOY B2®), other nickel-chromium alloys, other nickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper alloys, other nickel-tungsten or tungsten alloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like); platinum enriched stainless steel; titanium; combinations thereof; and the like; or any other suitable material.

As alluded to herein, within the family of commercially available nickel-titanium or nitinol alloys, is a category designated “linear elastic” or “non-super-elastic” which, although may be similar in chemistry to conventional shape memory and super elastic varieties, may exhibit distinct and useful mechanical properties. Linear elastic and/or non-super-elastic nitinol may be distinguished from super elastic nitinol in that the linear elastic and/or non-super-elastic nitinol does not display a substantial “superelastic plateau” or “flag region” in its stress/strain curve like super elastic nitinol does. Instead, in the linear elastic and/or non-super-elastic nitinol, as recoverable strain increases, the stress continues to increase in a substantially linear, or a somewhat, but not necessarily entirely linear relationship until plastic deformation begins or at least in a relationship that is more linear that the super elastic plateau and/or flag region that may be seen with super elastic nitinol. Thus, for the purposes of this disclosure linear elastic and/or non-super-elastic nitinol may also be termed “substantially” linear elastic and/or non-super-elastic nitinol.

In some cases, linear elastic and/or non-super-elastic nitinol may also be distinguishable from super elastic nitinol in that linear elastic and/or non-super-elastic nitinol may accept up to about 2-5% strain while remaining substantially elastic (e.g., before plastically deforming) whereas super elastic nitinol may accept up to about 8% strain before plastically deforming. Both of these materials can be distinguished from other linear elastic materials such as stainless steel (that can also can be distinguished based on its composition), which may accept only about 0.2 to 0.44 percent strain before plastically deforming.

In some embodiments, the linear elastic and/or non-super-elastic nickel-titanium alloy is an alloy that does not show any martensite/austenite phase changes that are detectable by differential scanning calorimetry (DSC) and dynamic metal thermal analysis (DMTA) analysis over a large temperature range. For example, in some embodiments, there may be no martensite/austenite phase changes detectable by DSC and DMTA analysis in the range of about −60 degrees Celsius (° C.) to about 120° C. in the linear elastic and/or non-super-elastic nickel-titanium alloy. The mechanical bending properties of such material may therefore be generally inert to the effect of temperature over this very broad range of temperature. In some embodiments, the mechanical bending properties of the linear elastic and/or non-super-elastic nickel-titanium alloy at ambient or room temperature are substantially the same as the mechanical properties at body temperature, for example, in that they do not display a super-elastic plateau and/or flag region. In other words, across a broad temperature range, the linear elastic and/or non-super-elastic nickel-titanium alloy maintains its linear elastic and/or non-super-elastic characteristics and/or properties.

In some embodiments, the linear elastic and/or non-super-elastic nickel-titanium alloy may be in the range of about 50 to about 60 weight percent nickel, with the remainder being essentially titanium. In some embodiments, the composition is in the range of about 54 to about 57 weight percent nickel. One example of a suitable nickel-titanium alloy is FHP-NT alloy commercially available from Furukawa Techno Material Co. of Kanagawa, Japan. Some examples of nickel titanium alloys are disclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which are incorporated herein by reference. Other suitable materials may include ULTANIUM™ (available from Neo-Metrics) and GUM METAL™ (available from Toyota). In some other embodiments, a superelastic alloy, for example a superelastic nitinol can be used to achieve desired properties.

In at least some embodiments, portions or all of tubular member 12 may also be doped with, made of, or otherwise include a radiopaque material. Radiopaque materials are understood to be materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. This relatively bright image aids the user of guidewire 10 in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with a radiopaque filler, and the like. Additionally, other radiopaque marker bands and/or coils may also be incorporated into the design of guidewire 10 to achieve the same result.

In some embodiments, a degree of Magnetic Resonance Imaging (MRI) compatibility is imparted into guidewire 10. For example, tubular member 12 or portions thereof may be made of a material that does not substantially distort the image and create substantial artifacts (i.e., gaps in the image). Certain ferromagnetic materials, for example, may not be suitable because they may create artifacts in an MRI image. Tubular member 12, or portions thereof, may also be made from a material that the MRI machine can image. Some materials that exhibit these characteristics include, for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nitinol, and the like, and others.

A sheath or covering (not shown) may be disposed over portions or all of tubular member 12 that may define a generally smooth outer surface for guidewire 10. In other embodiments, however, such a sheath or covering may be absent from a portion of all of guidewire 10, such that tubular member 12 may form the outer surface. The sheath may be made from a polymer or other suitable material. Some examples of suitable polymers may include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM, for example, DELRIN® available from DuPont), polyether block ester, polyurethane (for example, Polyurethane 85A), polypropylene (PP), polyvinylchloride (PVC), polyether-ester (for example, ARNITEL® available from DSM Engineering Plastics), ether or ester based copolymers (for example, butylene/poly(alkylene ether) phthalate and/or other polyester elastomers such as HYTREL® available from DuPont), polyamide (for example, DURETHAN® available from Bayer or CRISTAMID® available from Elf Atochem), elastomeric polyamides, block polyamide/ethers, polyether block amide (PEBA, for example available under the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), Marlex high-density polyethylene, Marlex low-density polyethylene, linear low density polyethylene (for example REXELL®), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly paraphenylene terephthalamide (for example, KEVLAR®), polysulfone, nylon, nylon-12 (such as GRILAMID® available from EMS American Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC), poly(styrene-b-isobutylene-b-styrene) (for example, SIBS and/or SIBS 50A), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers thereof, polymer/metal composites, and the like. In some embodiments the sheath can be blended with a liquid crystal polymer (LCP). For example, the mixture can contain up to about 6 percent LCP.

In some embodiments, the exterior surface of the guidewire 10 (including, for example, the exterior surface of tubular member 12) may be sandblasted, beadblasted, sodium bicarbonate-blasted, electropolished, etc. In these as well as in some other embodiments, a coating, for example a lubricious, a hydrophilic, a protective, or other type of coating may be applied over portions or all of the sheath, or in embodiments without a sheath over portion of tubular member 12, or other portions of guidewire 10. Alternatively, the sheath may comprise a lubricious, hydrophilic, protective, or other type of coating. Hydrophobic coatings such as fluoropolymers provide a dry lubricity which improves guidewire handling and device exchanges. Lubricious coatings improve steerability and improve lesion crossing capability. Suitable lubricious polymers are well known in the art and may include silicone and the like, hydrophilic polymers such as high-density polyethylene (HDPE), polytetrafluoroethylene (PTFE), polyarylene oxides, polyvinylpyrolidones, polyvinylalcohols, hydroxy alkyl cellulosics, algins, saccharides, caprolactones, and the like, and mixtures and combinations thereof. Hydrophilic polymers may be blended among themselves or with formulated amounts of water insoluble compounds (including some polymers) to yield coatings with suitable lubricity, bonding, and solubility. Some other examples of such coatings and materials and methods used to create such coatings can be found in U.S. Pat. Nos. 6,139,510 and 5,772,609, which are incorporated herein by reference.

The coating and/or sheath may be formed, for example, by coating, extrusion, co-extrusion, interrupted layer co-extrusion (ILC), or fusing several segments end-to-end. The layer may have a uniform stiffness or a gradual reduction in stiffness from the proximal end to the distal end thereof. The gradual reduction in stiffness may be continuous as by ILC or may be stepped as by fusing together separate extruded tubular segments. The outer layer may be impregnated with a radiopaque filler material to facilitate radiographic visualization. Those skilled in the art will recognize that these materials can vary widely without deviating from the scope of the present invention.

Various embodiments of arrangements and configurations of slots are also contemplated that may be used in addition to what is described above or may be used in alternate embodiments. For simplicity purposes, the following disclosure makes reference to guidewire 10, slots 18, and tubular member 12. However, it can be appreciated that these variations may also be utilized for other slots and/or tubular members. In some embodiments, at least some, if not all of slots 18 are disposed at the same or a similar angle with respect to the longitudinal axis of tubular member 12. As shown, slots 18 can be disposed at an angle that is perpendicular, or substantially perpendicular, and/or can be characterized as being disposed in a plane that is normal to the longitudinal axis of tubular member 12. However, in other embodiments, slots 18 can be disposed at an angle that is not perpendicular, and/or can be characterized as being disposed in a plane that is not normal to the longitudinal axis of tubular member 12. Additionally, a group of one or more slots 18 may be disposed at different angles relative to another group of one or more slots 18. The distribution and/or configuration of slots 18 can also include, to the extent applicable, any of those disclosed in U.S. Pat. Publication No. US 2004/0181174, the entire disclosure of which is herein incorporated by reference.

Slots 18 may be provided to enhance the flexibility of tubular member 12 while still allowing for suitable torque transmission characteristics. Slots 18 may be formed such that one or more rings and/or tube segments interconnected by one or more segments and/or beams that are formed in tubular member 12, and such tube segments and beams may include portions of tubular member 12 that remain after slots 18 are formed in the body of tubular member 12. Such an interconnected structure may act to maintain a relatively high degree of torsional stiffness, while maintaining a desired level of lateral flexibility. In some embodiments, some adjacent slots 18 can be formed such that they include portions that overlap with each other about the circumference of tubular member 12. In other embodiments, some adjacent slots 18 can be disposed such that they do not necessarily overlap with each other, but are disposed in a pattern that provides the desired degree of lateral flexibility.

Additionally, slots 18 can be arranged along the length of, or about the circumference of, tubular member 12 to achieve desired properties. For example, adjacent slots 18, or groups of slots 18, can be arranged in a symmetrical pattern, such as being disposed essentially equally on opposite sides about the circumference of tubular member 12, or can be rotated by an angle relative to each other about the axis of tubular member 12. Additionally, adjacent slots 18, or groups of slots 18, may be equally spaced along the length of tubular member 12, or can be arranged in an increasing or decreasing density pattern, or can be arranged in a non-symmetric or irregular pattern. Other characteristics, such as slot size, slot shape, and/or slot angle with respect to the longitudinal axis of tubular member 12, can also be varied along the length of tubular member 12 in order to vary the flexibility or other properties. In other embodiments, moreover, it is contemplated that the portions of the tubular member, such as a proximal section, or a distal section, or the entire tubular member 12, may not include any such slots 18.

As suggested herein, slots 18 may be formed in groups of two, three, four, five, or more slots 18, which may be located at substantially the same location along the axis of tubular member 12. Alternatively, a single slot 18 may be disposed at some or all of these locations. Within the groups of slots 18, there may be included slots 18 that are equal in size (i.e., span the same circumferential distance around tubular member 12). In some of these as well as other embodiments, at least some slots 18 in a group are unequal in size (i.e., span a different circumferential distance around tubular member 12). Longitudinally adjacent groups of slots 18 may have the same or different configurations. For example, some embodiments of tubular member 12 include slots 18 that are equal in size in a first group and then unequally sized in an adjacent group. It can be appreciated that in groups that have two slots 18 that are equal in size and are symmetrically disposed around the tube circumference, the centroid of the pair of beams (i.e., the portion of tubular member 12 remaining after slots 18 are formed therein) is coincident with the central axis of tubular member 12. Conversely, in groups that have two slots 18 that are unequal in size and whose centroids are directly opposed on the tube circumference, the centroid of the pair of beams can be offset from the central axis of tubular member 12. Some embodiments of tubular member 12 include only slot groups with centroids that are coincident with the central axis of the tubular member 12, only slot groups with centroids that are offset from the central axis of tubular member 12, or slot groups with centroids that are coincident with the central axis of tubular member 12 in a first group and offset from the central axis of tubular member 12 in another group. The amount of offset may vary depending on the depth (or length) of slots 18 and can include other suitable distances.

Slots 18 can be formed by methods such as micro-machining, saw-cutting (e.g., using a diamond grit embedded semiconductor dicing blade), electron discharge machining, grinding, milling, casting, molding, chemically etching or treating, or other known methods, and the like. In some such embodiments, the structure of the tubular member 12 is formed by cutting and/or removing portions of the tube to form slots 18. Some example embodiments of appropriate micromachining methods and other cutting methods, and structures for tubular members including slots and medical devices including tubular members are disclosed in U.S. Pat. Publication Nos. 2003/0069522 and 2004/0181174-A2; and U.S. Pat. Nos. 6,766,720; and 6,579,246, the entire disclosures of which are herein incorporated by reference. Some example embodiments of etching processes are described in U.S. Pat. No. 5,106,455, the entire disclosure of which is herein incorporated by reference. It should be noted that the methods for manufacturing guidewire 110 may include forming slots 18 tubular member 12 using these or other manufacturing steps.

In at least some embodiments, slots 18 may be formed in tubular member using a laser cutting process. The laser cutting process may include a suitable laser and/or laser cutting apparatus. For example, the laser cutting process may utilize a fiber laser. Utilizing processes like laser cutting may be desirable for a number of reasons. For example, laser cutting processes may allow tubular member 12 to be cut into a number of different cutting patterns in a precisely controlled manner. This may include variations in the slot width, ring width, beam height and/or width, etc. Furthermore, changes to the cutting pattern can be made without the need to replace the cutting instrument (e.g., blade). This may also allow smaller tubes (e.g., having a smaller outer diameter) to be used to form tubular member 12 without being limited by a minimum cutting blade size. Consequently, tubular member 12 may be fabricated for use in neurological devices or other devices where a relatively small size may be desired.

It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the invention. This may include, to the extent that it is appropriate, the use of any of the features of one example embodiment being used in other embodiments. The invention's scope is, of course, defined in the language in which the appended claims are expressed. 

What is claimed is:
 1. A method for calculating fractional flow reserve, the method comprising: advancing a pressure sensing guidewire through a body lumen to a first position distal of an intravascular occlusion; determining a distal pressure within the body lumen with the pressure sensing guidewire; proximally shifting the pressure sensing guidewire to a second position proximal of the intravascular occlusion; determining a proximal pressure within the body lumen with the pressure sensing guidewire; measuring an aortic pressure; calculating a pressure drift, wherein the pressure drift is the difference between the aortic pressure and the proximal pressure; and calculating a drift-compensated fractional flow reserve, wherein the drift-compensated fraction flow reserve corresponds to (the distal pressure+the pressure drift) divided by the aortic pressure.
 2. The method of claim 1, further comprising displaying the drift-compensated fraction flow reserve on a display unit.
 3. The method of claim 1, further comprising shifting the pressure sensing guidewire back to the first position and determining a second distal pressure within the body lumen with the pressure sensing guidewire.
 4. The method of claim 3, further comprising shifting the pressure sensing guidewire back to the second position and determining a second proximal pressure within the body lumen with the pressure sensing guidewire.
 5. The method of claim 4, further comprising calculating a second pressure drift, wherein the second pressure drift is the difference between the aortic pressure and the second proximal pressure.
 6. The method of claim 1, wherein the pressure sensing guidewire includes an optical pressure sensor.
 7. The method of claim 1, wherein the pressure sensing guidewire includes a Fabry-Perot pressure sensor.
 8. The method of claim 1, wherein the pressure sensing guidewire includes a piezoelectric pressure sensor.
 9. The method of claim 1, wherein the pressure sensing guidewire includes a proximal shaft portion and a distal shaft portion, the distal shaft portion having a plurality of slots formed therein.
 10. The method of claim 9, wherein the distal shaft portion has a variable inner diameter.
 11. The method of claim 1, wherein the pressure sensing guidewire includes a pressure sensor and wherein advancing the pressure sensing guidewire through a blood vessel to a first position distal of an intravascular occlusion includes advancing the pressure sensing guidewire through a guide catheter to a location where the pressure sensor is disposed distal of a distal end of the guide catheter.
 12. The method of claim 1, wherein measuring an aortic pressure includes measuring the aortic pressure with a second pressure sensing medical device.
 13. A method for calculating fractional flow reserve, the method comprising: advancing a pressure sensing guidewire through a body lumen of a patient to a first position proximal of an intravascular occlusion; determining a first proximal pressure within the body lumen with the pressure sensing guidewire; measuring an aortic pressure within the patient; equalizing the first proximal pressure with the aortic pressure; advancing the pressure sensing guidewire to a distal position that is distal of the intravascular occlusion; determining a distal pressure within the body lumen with the pressure sensing guidewire; proximally shifting the pressure sensing guidewire to the first position; determining a second proximal pressure within the body lumen with the pressure sensing guidewire; calculating a pressure drift, wherein the pressure drift is the difference between the second proximal pressure and the aortic pressure; and calculating drift-compensated fractional flow reserve, wherein the drift-compensated fraction flow reserve corresponds to (the distal pressure+the pressure drift) divided by the aortic pressure.
 14. The method of claim 13, wherein measuring an aortic pressure within the patient includes measuring the aortic pressure with a pressure sensing medical device inserted within the patient.
 15. The method of claim 13, further comprising displaying the drift-compensated fraction flow reserve on a display unit.
 16. The method of claim 13, wherein the pressure sensing guidewire includes an optical pressure sensor.
 17. The method of claim 13, wherein the pressure sensing guidewire includes a Fabry-Perot pressure sensor.
 18. The method of claim 13, wherein the pressure sensing guidewire includes a proximal shaft portion and a distal shaft portion, the distal shaft portion having a plurality of slots formed therein.
 19. A fractional flow reserve system, comprising: a pressure sensing guidewire including a pressure sensor; a control unit capable of processing pressure information from the pressure sensor and outputting drift-compensated fractional flow reserve corresponding to (a downstream pressure measured by the pressure sensor+a pressure drift) divided by an aortic pressure of a patient.
 20. The system of claim 19, wherein the pressure sensor includes an optical pressure sensor. 